Friday, November 6, 2015

Gravid female (left) and two more oak leaf itch mites (top and lower center) feeding on the (brownish) larvae of a gall-making fly, Macrodiplosis erubescens. The balloon-like structure on the female is the swollen abdomen full of eggs. Photo by Rick Grantham, OK State University.

The oak leaf itch mite, Pyemotes herfsi, is cousin to the straw itch mite--a predatory mite often associated with stored grain and stored grain insects, and known to bite people who come in contact with infested grain (if you've never heard of this or straw itch mite, check out the Mallis Handbook of Pest Control). It was first reported in the U.S. from Kansas in 2004, a year when the mite was unusually abundant and resulted in thousands of biting complaints from people working and playing outdoors. That same year the mite was found in Nebraska, Missouri and here in Texas.

The mite's normal home is inside of leaf galls found on trees, and it is best known from marginal leaf curl galls caused by a midge (Macrodiplosis erubescens) on oaks. It may be equally at home in other types of galls on different trees. The problem with this mite seems to occur mostly in late summer and fall, when mites are prone to dropping from trees. Although the mites are principally predators on insects, if they come in contact with skin they will bite, leaving a painful, itchy welt. For more information on the mites click here for a Nebraska fact sheet.

Bites from the oak leaf itch mite are typically seen on the neckor shoulder region of people who have been outdoors undertrees with galls.

This little mite has a history in Texas too. In October, 2004 the Dallas area had what was believed to be a mini-outbreak of these mites, when Dallas County Health and Human Services received a number of complaints from schools concerning "bug bites" among students and staff--apparently from playgrounds. At that time DCHHS staff and I sampled leaves from a number of school campus trees and isolated a single oak leaf itch mite, confirming at least the presence of these mites in north Texas. The rash of bite cases was assumed due to this mite by DCHHS in its December 2004 monthly report of epidemiology activity. No remarkable incidents of these bite complaints have recurred since 2004, although a few suspect calls have been received this year.

These mites are very small (0.2 mm-long) and difficult to find. Bites, when they occur, tend to be around necks and shoulders, implying that the mites bite when they land, and do not crawl much on the skin before biting, like ticks or chiggers.

Complaints about mystery bites are one of the most common and frustrating calls for PMPs. But if the complaints come from a client who has been spending time outdoors, and especially under trees that are shedding their leaves, this is one critter to keep in mind.

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About Me

I have served as entomology specialist for Texas AgriLife Extension since 1989. I get to work with, and for, a bunch of great people including pest management professionals, school facilities managers, extension volunteers, researchers and other extension professionals. My areas of specialty center on research on insects affecting man including spiders, scorpions, fire ants, termites and others. My program also focuses on training school maintenance professionals in principles of integrated pest management (IPM). Our goal is to make schools healthier, cleaner places to study and live.